This invention relates generally to gas turbine engines, and more specifically to methods and apparatus for operating gas turbine engines.
Gas turbine engines generally include, in serial flow arrangement, a high-pressure compressor for compressing air flowing through the engine, a combustor in which fuel is mixed with the compressed air and ignited to form a high temperature gas stream, and a high pressure turbine. The high-pressure compressor, combustor and high-pressure turbine are sometimes collectively referred to as the core engine. Such gas turbine engines also may include a low-pressure compressor, or booster, for supplying compressed air to the high pressure compressor.
Gas turbine engines are used in many applications, including in aircraft, power generation, and marine applications. The desired engine operating characteristics vary, of course, from application to application. More particularly, when the engine is operated in an environment in which the ambient temperature is reduced in comparison to other environments, the engine may be capable of operating with a higher shaft horse power (SHP) and an increased output, without increasing the core engine temperature to unacceptably high levels. However, if the ambient temperature is increased, the core engine temperature may rise to an unacceptably high level if a high SHP output is being delivered.
To facilitate meeting operating demands, even when the engine ambient temperature is high, e.g., on hot days, at least some known gas turbine engines include inlet system evaporative coolers or refrigeration systems to facilitate reducing the inlet air temperature. At least some known systems use water spray fogging or injection devices to inject water into either the booster or the compressor to facilitate reducing the operating temperature of the engine.
For example, at least one gas turbine includes a booster compressor to facilitate increasing the pressure of the air entering the high pressure compressor, which results in increased power output and efficiency of the gas turbine engine. An intercooler heat exchanger may be positioned between the booster compressor and the high pressure compressor to facilitate reducing the temperature of the air entering the high pressure compressor. Using an intercooler facilitates increasing the efficiency of the engine while reducing the quantity of work performed by the high pressure compressor. At least one known intercooler heat exchanger uses ambient air or water as a cooling medium to cool the air flow exiting the booster compressor. When water is used as the cooling medium, heat from the water is rejected using water cooled cooling towers. Accordingly, the reduction in temperature is limited by the dry bulb ambient air temperature for the air cooled heat exchanger and by the wet bulb temperature for the water cooled heat exchanger. However, air-to-water heat exchangers typically use relatively large quantities of water which may not be available in more arid regions. Furthermore, air-to-air heat exchangers are generally less effective when used on hot days due to a lower air density and an increase in the intercooler exit temperatures, thus resulting in a decrease in the gas turbine power.